NSFetchResultController Delegate Error - iphone

Question

I have a couple of UIViewControllers that show a table view of my 'User' objects as the section, and 'Site' objects as rows under each section. The Site to User relationship is one-to-many.
At the moment I am showing this data with the following code:
- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView {
id <NSFetchedResultsSectionInfo> sectionInfo = [[self.fetchedResultsController sections] objectAtIndex:0];
return [sectionInfo numberOfObjects];
}
- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section {
User *sectionUser = (User*)[self.fetchedResultsController objectAtIndexPath:[NSIndexPath indexPathForRow:section inSection:0]];
return [[sectionUser.sitesToUser allObjects] count];
}
In my NSFetchResultsController I'm just pulling all User objects, nothing special.
Now my issue - whenever I update the results, by removing a section (ie a User) or adding a User whilst this view is also open, I get an NSFetchedResultsController delegate error:
Serious application error. An exception was caught from the delegate of
NSFetchedResultsController during a call to -controllerDidChangeContent:. Invalid
update: invalid number of sections. The number of sections contained in the table
view after the update (2) must be equal to the number of sections contained in the
table view before the update (1), plus or minus the number of sections inserted or
deleted (0 inserted, 0 deleted). with userInfo (null)
I only get it in the views where I am displaying my data in this way, is User is section, Site/s are rows under each section.
Am I doing something really stupid? I thought it would just remove the section when I delete it etc... Seems to work fine if each User is a ROW in the UITableView - which I believe is the crux of my issue...

Answer 1

I'm using Core Data but my code for numberOfSectionsInTableView: and tableView:numberOfRowsInSection: method is different... I don't know if this can solve your problem but, try to use this code:
-(NSInteger)numberOfSectionsInTableView:(UITableView *)tableView
{
return [[self.fetchedResultsController sections] count];
}
-(NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
NSInteger rowsNumber = 0;
id <NSFetchedResultsSectionInfo> sectionInfo = [[self.fetchedResultsController sections] objectAtIndex:section];
rowsNumber = [sectionInfo numberOfObjects];
return rowsNumber;
}
For the sections, I've never used it but try to work on the sectionNameKeyPath argument of the initWithFetchRequest:managedObjectContext:sectionNameKeyPath:cacheName: when you initialize your controller.

Answer 2

You haven't shown your fetchedResultsController delegate calls:
- (void)controllerWillChangeContent:(NSFetchedResultsController *)controller
- (void)controllerDidChangeContent:(NSFetchedResultsController *)controller
- (void)controller:didChangeObject:atIndexPath:forChangeType:newIndexPath
- (void)controller:didChangeSection:sectionInfoAtIndex:forChangeType:
These calls are responsible for adding and removing the rows / sections from your table so everything "adds up" as far as the tableview is concerned.
In your case you are kind of "abusing" what a section is so this code could get tricky.
If you are prepared to do without animation you could just implement:
-(void)controllerDidChangeContent:(NSFetchedResultsController*) controller {
[self.tableView reloadData];
}
Daniel.